Frequency Modulation represents a system of radio transmission in which the carrier wave is modulated so that its frequency varies with the audio signals being transmitted. The first workable system for radio communication was described by the American inventor Edwin H. Armstrong in 1936.
Frequency modulation has several advantages over the system of amplitude modulation (AM) used in the alternate form of radio broadcasting. The most important of these advantages is that an FM system has greater freedom from interference and static. Various electrical disturbances, such as those caused by thunderstorms and automobile ignition systems; create amplitude modulated radio signals that are received as noise by AM receivers. A well-designed FM receiver is not sensitive to such disturbances when it is tuned to an FM signal of sufficient strength. Also, the signal-to-noise ratio in an FM system is much higher than that of an AM system. Finally, FM broadcasting stations can be operated in the very-high-frequency bands at which AM interference is frequently severe; commercial FM radio stations are assigned frequencies between 88 and 108 MHz The range of transmission on these bands is limited so that stations operating on the same frequency can be located within a few hundred miles of one another without mutual interference.
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